Even though crop plants are growing under sufficient soil moisture conditions, stomatal conductance and photosynthetic rate decrease in the afternoon on a clear day and, moreover, severe leaf wilting and leaf death sometimes occur due to water deficits. Increase of resistance to water transport in plants is responsible for the plant water deficits. It is required to estimate resistance to water transport in various parts of a plant for investigating the cause of the water deficits and for breeding drought-resistant plants. This investigation was to develop a simple method for measuring the resistance in crop plants especially in roots and stem of which resistance is thought to be variable.1. For estimating stem resistance, (1) low hydrostatic pressure (P) was applied on the cut end of a stem segment, (2) exudation rate (E) from the other cut end of the segment was measured and (3) resistance to water transport in the segment (Rs) was calculated by Eq(1). Resistance of the base of a ste
… Morem and of the panicle base increased markedly in the severely wilted cucumber plant and in the rice plant with desiccated white head, respectively, which agrees with the results obtained from other reliable measurements. It was concluded that this method can be employed for estimating stem resistance.Rs=P/E (1), Rr=Pr/Er (2)2. For estimating root resistance, (1) exudation rate (Er) and root pressure (Pr) were measured at the base of a stem and the resistance from roots to the base of a stem was calculated by Eq. (2). This resistance can be thought to be root resistance in active water uptake. Root resistance in active water uptake was far larger than that in passive water uptake under intense transpiration. However, it was supposed that there is a close correlation between the resistance in active and passive water uptake, that is, the higher the resistance in active water uptake, the higher, the resistance in passive water uptake. It was concluded from these results that root resistance in passive water uptake under intense transpiration could be compared by measuring the resistance in active water uptake. Less